The subject of the present invention is a refrigerating compressor with variable-speed coils.
The document FR 2 885 966 describes a coil compressor, also known as a scroll compressor, comprising a sealed chamber delimited by a shell and containing a suction volume and a compression volume arranged respectively either side of a body contained in the chamber. The shell delimiting the sealed chamber comprises a refrigerating gas inlet.
An electric motor is positioned inside the sealed chamber, with a stator located on the outside, mounted fixed relative to the shell, and a rotor in a central position, joined to a drive shaft, in the form of a crank shaft, a first end of which drives an oil pump feeding, from oil contained in a pan situated in the bottom part of the chamber, a lubrication pipe provided in the central part of the shaft. The lubrication pipe comprises lubrication orifices level with the various bearings guiding the drive shaft.
The compression volume contains a compression stage comprising a fixed volute fitted with a coil engaged in a coil of a moving volute, the two coils delimiting at least one compression chamber of variable volume. The second end of the drive shaft is fitted with an eccentric driving the moving volute in an orbital movement, to compress the refrigerating gas that is sucked in.
From a practical point of view, the refrigerating gas arrives from outside and penetrates into the sealed chamber. A portion of the gas is directly sucked in towards the compression volume, whereas the other portion of the gas passes through the motor before flowing towards the compression stage. All of the gas arriving either directly at the compression stage, or after passage through the motor, is sucked in by the compression stage, penetrating into at least one compression chamber delimited by the two coils, the inlet being at the periphery of the compression stage, and the gas being conveyed to the center of the coils as and when compression occurs by reduction of the volume of the compression chambers, resulting from the movement of the moving volute relative to the fixed volute. The compressed gas leaves in the central part towards the compressed gas recovery chamber.
According to the internal flow conditions of this type of compressor, the refrigerating gas entering into the compressor can be charged with oil, and this oil can originate, for example, from leaks from the bearings, from scrubbing of the surface of the oil pan by the gas.
It should be noted that the oil ratio in the refrigerating gas changes according to the rotation speed of the rotor of the electric motor.
Thus, at low rotor rotation speed, the quantity of oil circulating with the refrigerating gas is low, which can degrade the performance of the compressor and reduce the lubrication of the various parts of the compressor.
On the other hand, at high rotor rotation speed, the oil ratio in the refrigerating gas leaving the compressor can become excessive. The direct consequence of this excessive oil ratio in the gas is loss of efficiency of the heat exchange of the exchangers located downstream of the compressor, given the fact that the oil droplets contained in the gas have a tendency to be deposited on the exchangers and form a layer of oil on the latter.
Furthermore, an excessive oil ratio in the gas can also cause the oil pan to empty, which could lead to the destruction of the compressor.